Many work machines are in use that use multi-component linkages to position and manipulate implements that act on work material. In a typical two member linkage arrangement, a lift boom is pivotally connected at one end to an upper frame of the work machine, and pivotally connected at the other end to a stick boom. The implement is pivotally connected to the end of the stick boom opposite the connection to the lift boom. A lift cylinder connected between the upper frame and the lift boom is extended and retracted to raise and lower the lift boom, and an extension cylinder connected between the lift boom and the stick boom is extended and retracted to pivot the stick boom away from and back toward the lift boom. An additional implement cylinder connected between the stick boom and the implement, perhaps by an intermediate linkage connection, extends and retracts to move the implement relative to the stick boom. The components act together under the control of the operator to move the implement through a range of motion defined by the movements of the components to allow the implement to perform the material handling functions for which the work machine is designed.
Multi-component linkages such as that described above are implemented in many different work machines performing a variety of material handling functions. For example, multi-component linkages are implemented in backhoe loaders, material handlers, skidders, wheeled and tracked excavators, telehandlers, forwarders, forest machines, tracked feller bunchers, knuckle boom loaders, wheeled and tracked harvesters, and the like. In forestry work machines, such as, for example, feller bunchers, the multi-component linkages provide versatility in manipulating the implement that is necessary to effectively operate the work machines in diverse conditions that may be encountered at job sites. A feller buncher includes an implement that rapidly cuts and gathers several trees before felling them. The tree-grabbing implement of the feller buncher is provided with a chain-saw, circular saw or shearing/pinching device designed to cut trees off at the base. The tree-grabbing implement is then manipulated to place the cut tree(s) on a stack suitable for a skidder, forwarder or other work machine to transport the trees for further processing.
In known feller bunchers, the operator uses controls for the lift cylinder, the stick cylinder and the implement cylinder to orient the implement and move the implement to a tree to be cut down. When the feller buncher is operated on a generally horizontal grade at the work site, the operator manipulates all three controls to position the implement close to the ground, and then extend the lift boom and stick boom to move the implement parallel to the ground and into engagement with tree. Control of the feller buncher on a sloped grade is more difficult for the operator. When, for example, the feller buncher is facing uphill, the operator can operate the controls to move the implement upward parallel to the sloped surface in a similar manner as with the flat surface. This allows the operator to move the implement in a similar manner regardless of the slope on which the feller buncher is disposed. However, cutting upwardly into the tree can result in pinch points on the saw blade as the weight of the tree rotates back toward the feller buncher. The pinching can be reduced or eliminated by orienting and moving the tree-grabbing implement horizontally with respect to gravity to the tree instead of parallel to the ground. However, manipulating three controls to produce the horizontal movement of the implement on a sloped grade and maintaining the orientation of the implement is more difficult for the operator to execute, and extended periods of attempting to control the movement can be more fatiguing to the operator.
Feller bunchers and other types of work machines with multi-component linkages have been developed to assist the operators in creating specified movements of the linkages and implements, and to adapt to operation on sloped surfaces as described above. For example, U.S. Pat. No. 6,443,196, issued to Kurelek on Sep. 3, 2002 and entitled, “Hydraulic Circuits for Tree-Harvesting Knuckle Booms,” discloses two boom members and hydraulic cylinders of a knuckle boom tree harvesting machine arranged and proportioned so that with a single control movement during reaching and retracting actions, the working tool head is made to travel in an approximately horizontal path. The cylinder diameters and strokes are dimensioned and control valve is so connected to the cylinders that during the horizontal reaching action load-supporting pressurized oil from a collapsing cylinder is not required to be drained to the reservoir in the conventional heat generating manner, but is rather shunted directly to an extending cylinder where it continues to do useful load support work. An additional reach cylinder is provided to between the hoist boom and stick boom to alter or hold the angle between the booms. Consequently, additional components are required to implement the hydraulic circuits. Moreover, the publication does not discuss the reaching and retracting actions provided by the hydraulic circuit arrangement when the knuckle boom harvesting machine is used on a sloped grade.
Another example of a modified forestry machine is provided in U.S. Pat. No. 8,180,532, issued to O'Halloran et al. on May 15, 2012 and entitled, “Vector Controlled Leveling System for a Forestry Machine.” The O'Halloran et al. reference discloses a leveling control system for a forestry machine employing position sensors that relay information about the orientation of the carriage in relation to the swing-house assembly in order to control roll and pitch in a manner that maximizes the operating envelop of the leveling mechanism. The angles of pitch and roll of the swing-house assembly in relation to the carriage are measured and/or calculated and a controller limits operation of the leveling mechanism to an operating envelop that may be described in terms of pitch and roll. The swing-house assembly orientation cylinders are decelerated gradually as the operating envelope is approached. The controller can include an automatic leveling mode. The controller can change the function of the fore, aft, left and right operator controls so that they are true from the operator's frame of reference regardless of the rotary position of the cab relative to the carriage. With this arrangement, the leveling system is operated to level the swing-house assembly as the carriage traverses uneven or sloping terrain. The leveling allows the operator to cause the implement to move horizontally on all surfaces using essentially the same operator control manipulations. However, as with the Kurelek reference, additional mechanical and hydraulic components are required in the design, adding to the complexity and failure modes for the work machine.
In view of the reconfiguration of existing work machines to implement the designs disclosed in the references, a need exists for a multi-component linkage and implement tracking mechanism for determining a sloped grade on which the work machine is operating and to causing the linkage to move the implement horizontally or vertically regardless of the slope of the surface over which the work machine is operating, and to maintain a prescribed orientation of the implement as it moves.